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1. Prevent the transfer of aluminum plating
1. Adopting special adhesive for aluminum film
Ordinary adhesive solvents have poor releasability, and the glue easily penetrates into the aluminized layer, which affects the fastness of the aluminized layer. If the drying effect is not good during compounding and there are too many residual solvents, the bonding strength will decrease after curing. Therefore, you should choose a special adhesive for aluminum coating with moderate molecular weight, good solvent release, relatively uniform coating, and low initial adhesion.
2. The amount of glue should be appropriate
If the amount of glue applied is too large, the drying effect of the drying tunnel is likely to be poor, the glue solution penetrates into the aluminum plating layer, and the curing time is extended, and the migration phenomenon of the aluminum plating layer is likely to occur. Therefore, the amount of glue should be controlled within an appropriate range. According to experience, it is generally appropriate to control within 2g / m 2 -2.5g / m 2.
3. Loss of curing agent
Improve the flexibility of the adhesive layer, can also effectively prevent the phenomenon of aluminum plating transfer. In the past, the method of reducing the amount of curing agent was usually adopted. If the special adhesive for aluminum plating is selected, the normal ratio can be used.
4. Increase the drying temperature and wind speed of the drying tunnel
During the composite processing of aluminum coating, the drying temperature of the drying tunnel should be appropriately increased, such as increasing 50 C-10 0 C, and ensuring that the wind speed is above 5m / s (if the equipment conditions are available) to make the solvent evaporate more thoroughly Some, reduce the residual amount of solvent to prevent the transfer of aluminum coating. In addition, the use of high wire roller and high concentration coating also has certain effects.
5. Increase curing temperature and shorten curing time
Aluminized film composite products should properly increase the curing temperature and shorten the curing time during the curing process, so that the adhesive can reduce its penetration and damage to the aluminized layer, which is beneficial to prevent the transfer of the aluminized layer. It is generally controlled between 50 0 C-60 0 C for 24 hours-36 hours, avoiding long-term curing at low temperature.
6. Use good quality aluminum coating
If the cost permits, some products with higher requirements are better to choose aluminum plating with primer, which is currently produced by domestic manufacturers.
7. Prevent white spots on the composite film
Use ink of better quality to ensure that the adhesive is coated evenly, and the ink layer can be evenly infiltrated by the residual solvent. Choose an adhesive that has good coating performance for the ink and aluminum film used.
For lighter colors, especially white areas, the amount of glue should be increased appropriately.
A compound method of coating with aluminum coating is used, but it will aggravate the transfer of aluminum coating.
Second, prevent the tunnel phenomenon
1. Coordinate and control the tension of the main and auxiliary unwinding and drying tunnels, so that each layer of the composite film retracts simultaneously after cooling and solidification.
2. Increase the drying temperature and air speed of the drying tunnel to improve the initial viscosity.
3. Apply glue evenly to prevent local tunnel phenomenon.
4. Appropriate amount of glue to prevent slippage when too much glue or too much glue is present, which can cause tunnels.
5. The product after compounding should be placed at natural or low temperature for a period of time before compounding twice.
3. Prevent the disappearance of aluminum plating
The phenomenon that aluminum plating disappears is not uncommon. Some products have large areas of plaques in the middle aluminum plating layer after being placed for a period of time, and some products basically disappear after boiling and become transparent windows.
Reason: After vacuum evaporation, the pure aluminum is adsorbed on the surface of PET. It will be oxidized when exposed in the air, and it will also be oxidized when it is wet.
When aluminum is present as a monomer, the surface will be covered with a layer of aluminum oxide. Although aluminum is a more active metal, aluminum is more difficult to react with water. The reason is that one of the products that reacts with water is the insoluble substance AI (OH) 3. Under heating conditions, aluminum hydroxide will also be converted into alumina), the insoluble aluminum hydroxide (alumina) becomes a film covering the surface of aluminum will prevent aluminum from further reaction with water. The reaction will increase when heated or (and) in the presence of other media (such as CI-ions). The micro-magnetic field formed between aluminum and water may also contribute to its reaction. Due to the large number of substances in contact, aluminum complexes may also be formed.
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